1. Field of Invention
The present invention relates to an improved three-piece truck system for railroad cars that provides long travel constant contact side bearings for improved stability, a friction shoe having improved squareness, a resilient pedestal pad for improved curving performance and increased wear resistance, and a suspension system tuned and optimized for rail cars that improves ride quality, increases resistance to suspension bottoming, and increases hunting threshold speed. The motion control truck system is believed to meet or exceed recent American Association of Railroads (AAR) M-976 requirements.
2. Description of Related Art
Opposed ends of railway cars are commonly supported on spaced-apart truck assemblies that allow travel of the railway car along a railway track. A standard railway car includes a pair of railway car trucks that include a pair of sideframes supported on a pair of axles, each provided with a pair of wheels secured to each axle and spaced from each other by a distance corresponding to the gauge of the associated railway track. Side frames are longitudinally operable along the track and run parallel to the longitudinal axis of the rail car. Side frames include a top member, a compression member, a tension member, a column, a gib, a pedestal, and a pedestal roof.
A hollow bolster is transversely positioned to the longitudinal axis of the railway car, couples the sideframes, and has the car body supported thereon. A bolster center bowl is provided having a central opening. The bolster center bowl receives and supports a protruding circular center plate of a draft sill associated with a carbody. The truck center bowl provides the principal bearing surface to support the carbody on the truck bolster. Truck center bowls are often fitted with a horizontal wear plate and a vertical wear ring to improve wear characteristics and extend the service life of the associated truck bolster.
Each sideframe includes a window portion for bolster ends and spring groups supporting the bolster, which allows bolster movement relative to the sideframe. Each spring group typically includes a plurality of coil springs extending between a sideframe spring seat portion and an undersurface of the bolster end spaced above the respective sideframe spring-seat.
Side bearings may also be disposed between the truck bolster and carbody, typically provided laterally to each side of center plate bowl on bolster on the bearing pads. Constant contact side bearings are commonly used on railroad car trucks. They are typically located on the truck bolster, such as on side bearing pads, but may be located elsewhere. Some prior designs have used a single helical spring mounted between a base and a cap. Others use multiple helical springs or elastomer elements.
The size capacity of Association of American Railroads (AAR) standard freight car trucks are commonly indicated by nominal or rated load carrying capacity of a railway car equipped with such trucks. Typical truck size indications are 40 ton, 50 ton, 70 ton, 100 ton, and 125 ton. A more specific indication of truck size is the total allowable gross weight on rail of a railway car equipped with the particular size truck. Examples of such truck size indications are 142,000 lbs, 177,000 lbs, 220,000 lbs, 263,000 lbs, and 315,000 lbs, respectively. Since 1994, AAR standard freight car trucks have been commercially available for gross weight on rail railway cars with 286,000 pound ratings.
Total allowable or maximum gross weight on rail for a railway truck is generally determined by the capacity of the journal bearings on the associated railway truck axles. Also, associated with each nominal railway car truck size is a given wheel diameter size to limit maximum wheel/rail contact stress. Examples of typical journal bearing sizes and wheel sizes for AAR standard freight car trucks are included in the following table.
TABLE 1NominalMaximum GrossJournalWheel SizeTruck SizeWeight on RailBearing SizeDiameter40 ton142,000 lbs5 in × 9 in33 in50 ton177,000 lbs5.5 in × 10 in 33 in70 ton220,000 lbs 6 in × 11 in33 in100 ton 263,000 lbs6.5 in × 12 in 36 in125 ton 315,000 lbs 7 in × 12 in38 in
The Association of American Railroads (AAR) establishes the criteria for railcar stability, wheel loading and spring group structure. These criteria are set or defined in recognition that railcar body dynamic modes of vibration, such as rocking of sufficient magnitude, may compress individual springs of the spring group at alternate ends of the bolster, even to a solid or near-solid condition. This alternate-end spring compression is followed by an expansion of the springs, which action-reaction can amplify and exaggerate the “apparent” wheel loading on the suspension system and subsequent rocking motion of the railcar, as opposed to the actual or “average” weight or load from the railcar and therein. As a consequence of the amplified rocking motion, and at large amplitudes of such rocking motion, the contact force between the rails and the wheels can be dramatically reduced on the alternate lateral sides of the railcar. In an extreme case, the wheels can elevate and misalign from the track, which enhances the opportunity for a derailment.
There are various modes of motion of a railcar body, that is bounce, pitch, yaw, and lateral oscillation, as well as the above-noted roll. In car body roll, or twist and roll as defined by the AAR, the car body appears to be alternately rotating in the direction of either lateral side and about a longitudinal axis of the railcar. Car body pitch can be considered a forward to rearward rotational motion about a transverse railcar axis of rotation, such that the railcar may appear to be lunging between its forward and reverse longitudinal directions. Car body bounce refers to a vertical and linear motion of the railcar. Yaw is considered a rotational motion about a vertical axis extending through the railcar, which gives the appearance of the car ends moving to and fro as the railcar moves down a track. Finally, lateral stability is considered an oscillating lateral translation of the car body. Alternatively, truck hunting refers to a parallelogramming or warping of the railcar truck, not the railcar body, which is a separate phenomena distinct from the railcar body motions noted above. Truck hunting is also an oscillating lateral translation of the wheel sets due to the wheels being conical in cross section. All of these motion modes are undesirable and can lead to unacceptable railcar performance, as well as contributing to unsafe operation of the railcar.
A common apparatus utilized to control the dynamic responses of railcar trucks and bodies is a friction shoe assembly, which provides bolster-to-sideframe damping of oscillating motion. Friction shoes include a friction wedge in a bolster pocket in which the wedge is biased to maintain frictional engagement with the sideframe. Friction shoes dissipate suspension system energy by frictionally damping relative motion between the bolster and sideframe.
Friction shoes are most generally utilized with constant or fixed bias frictional damping structures with the friction shoes contacting complementary inner surfaces of the bolster pockets: A retention or control spring, which biases the friction shoe and maintains it against the bolster pocket surface and the sideframe column wear surface, is supported by the spring base or seat portion of the sideframe beneath the friction shoe. With a fixed or constant bias or damping spring group, the control springs do not carry load and the compression rate of the friction shoe assembly spring, that is the spring displacement as a function of the force, remains essentially unchanged during relative movement between the bolster and sideframe. Thus, in a constant bias arrangement, the biasing force applied to the friction shoe remains constant throughout the operating ranges for both the relative motion and biasing spring displacement between the bolster and sideframes for all conditions of railcar loading. Consequently, the frictional force between the friction shoe and column wear surfaces remains relatively constant.
Alternatively, the response of friction shoes in variable bias arrangements varies with the compressed length of the retention spring. Therefore, the frictional force between the friction shoe and the sideframe column varies with the vertical movement of the bolster. However, in a variable rate spring structure, the operating range, or the spring rate, of the control spring may not be adequate to respond to the applied forces, that is the railcar weight and the oscillating dynamic forces, from variations in the track and operating conditions. In at least some variable friction force arrangements, the distance between the friction shoe and the sideframe spring seat has been considered to be adequate to accommodate a friction-shoe biasing spring with a suitable design characteristic to handle the force variations and ranges in the railcar wheel-truck assembly, even for railcars with a higher-rated, load-bearing capacity.
In fixed or constant biasing arrangements, the friction shoe frequently has a spring pocket to receive a control spring having adequate length and coil diameter to provide the requisite frictional damping.
The spring group arrangements along with the friction shoes support the railcar and damp the relative interaction between the bolster and sideframe. There have been numerous types of spring groups utilized for railcar suspension systems, such as concentric springs within the spring group; five, seven and nine spring arrangements; elongated springs for the friction shoe; and, short spring-long spring combinations for the friction shoe within the multi-spring set. These are just a few of the many noted spring arrangements that have been positioned between sideframe and bolster end assemblies. These spring assemblies must conform to standards set by the Association of American Railroads (AAR), which prescribes a fixed spring height for each coil spring at the fully-compressed or solid spring condition. The particular spring arrangement for any railcar is dependent upon the physical structure of the railcar, its rated weight-carrying capacity and the structure of the wheel-truck assembly. That is, the spring group arrangement must be responsive to variations in the track as well as in the railcar such as the empty railcar weight, the laden-to-capacity railcar weight, railcar weight distribution, railcar operating characteristics, available vertical space between the sideframe spring-platform and the bolster end, the specific friction shoe design and, other operating and physical parameters.
Prior spring group designs have been limited to minimum reserve capacities of 1.5 per AAR standards S-259 and Rule 88. Although the minimum allowable reserve capacity is 1.5 per AAR standards, suspension reserve capacity for friction damped car suspensions has been reduced for railroad cars hauling automobiles, because they are equipped with their own suspensions. Reducing reserve capacity for these types of loads was considered acceptable to improve ride quality. With the exception of railroad cars hauling automobiles, the AAR minimum reserve capacity of 1.5 was thought to be the minimum allowable spring capacity to prevent suspension bottoming. However, the prior art did not consider the length of the car or the interaction of the suspension systems within a car. The same suspension design and damping was used for all car types.
The railcar must be physically able to bear the rated load weight and maintain contact with the track as the car travels at varying speeds along different track contours with varying track conditions. Simultaneously, the railcar and truck assemblies must have operating characteristics enabling it to be safely operable on these same varying track conditions at the unloaded, empty-car condition. Both operating weight extremes must be accommodated without posing the danger of imminent derailment for either condition.
To provide a railcar with the above-required operating range capabilities, the damping system spring group incorporated into the truck assembly must have certain static and dynamic operating characteristics. That is, operation of a car in motion on a rail track with a wide variant of track and contour conditions can lead to dynamic operating problems from oscillations, which can progress to uncontrolled instabilities of the railcar especially in super elevated curves. Track-to-wheel separation is a result of several conditions, including traversal of rail imperfections, and in conjunction with the oscillation frequency of the car from traversing the non-uniform tracks, disengagement of a wheel of an unloaded railcar is not an unusual condition. Although wheel disengagement from the track does not generally result in a derailment, the implied hazard from such a separation is readily apparent and should be avoided, if possible.
One of the primary methods for dealing with the oscillations of a railcar and truck assembly is the damping from the above-noted friction shoe, as well as the stabilizing effect of the supporting springs. These oscillations may be due in part to the physical track conditions experienced by railway cars during their operation. Variations in track conditions, for example, track joints, can affect operation of the truck assembly, which track variation effects may be amplified as they are transferred through the wheel, axle and suspension to the frame. This may affect operation of the railcar as it traverses the track and encounters more of these track-induced operating problems.
Typical side bearing arrangements are designed to control hunting of the railroad car. That is, as the semi-conical wheels of the railcar truck ride along a railroad track, a yaw axis motion is induced in the railroad car truck. As the truck yaws, part of the side bearing is made to slide across the underside of the railroad car body. The resulting friction produces an opposing torque that acts to prevent this yaw motion. Another purpose of railroad car truck side bearings is to control or limit the roll motion of the car body. Most prior side bearing designs limited travel of the bearings to about 5/16″. The maximum travel of such side bearings is specified by the Association of American Railroads (AAR) standards. Previous standards, such as M-948-77, limited travel to 5/16″ for many applications.
New standards have evolved that require railway car trucks to meet more stringent requirements. The most recent AAR standard is M-976, which is applicable to railway car having a gross rail load in excess of 268,000 lbs.